A major issue for plant genetic engineering is the extent to which transgenes can escape from cultivation and negatively impact the ecosystem. The pollen from transgenic plants may impart wild plants with better fitness or aid in transfer of genes of resistance especially during negative selections processes. This kind of gene flow is of particular concern in forest trees because trees are virtually undomesticated and are likely to be present within potential mating proximity of transgenic cultivated plants and trees, leading to contamination of the wild germplasm (DiFazio et al., Plantation Forest Biotechnology for the 21st Century, 2004, 405-422).
A reproductive tissue specific promoter offers a solution for containing the gene flow from transgenic trees into the wild. There are various mechanisms being developed to prevent gene flow from transgenic plants to related or wild germplasm. This includes the use of cytotoxic genes under the control of reproductive tissue specific promoters or the use of gene excision mechanisms at time of reproductive tissue development. Until now, very limited success has been achieved in controlling pollen production in trees. Recently, the PrMC2-barnaseH102E expression cassette was found to efficiently ablate pollen in tobacco, pine and eucalyptus. The field performance of the PrMC2-barnaseH102E in representative angiosperm and gymnosperm trees indicated that this cassette can be used to mitigate pollen-mediated gene flow concerns associated with large scale deployment of transgenic trees (Zhang et al. Plant Physiol., 2012, 159(4), 1319-1334).